A high m.w. form of decay-accelerating factor (DAF-2) exhibits size abnormalities in paroxysmal nocturnal...

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Decay-accelerating factor (DAF) is a 70,000 Mr membrane protein crucial for regulating the complement cascade on cell surfaces.
• DAF inhibits the amplification of complement activation, a key immune response pathway.

Purpose of the Study:

• To investigate the nature of decay-accelerating factor (DAF) and its potential variants.
• To characterize the DAF forms present on erythrocytes and their alterations in paroxysmal nocturnal hemoglobinuria (PNH).

Main Methods:

• Western blot analysis of red cell ghost proteins and partially purified DAF.
• Electrophoresis under denaturing conditions to assess protein size.
• Immunological detection using monoclonal antibodies against DAF epitopes.

Main Results:

• Monoclonal antibodies identified a second DAF polypeptide (DAF-2) at 140,000 Mr, distinct from the primary 70,000 Mr DAF (DAF-1).
• Both DAF-1 and DAF-2 exhibit complement decay-accelerating activity and membrane reincorporation.
• Erythrocytes from PNH patients lacked both DAF-1 and DAF-2, or showed a reduced size of DAF-2 in some cases.

Conclusions:

• DAF exists in at least two forms, DAF-1 and DAF-2, with similar functional properties.
• The absence or altered size of DAF-2 in PNH erythrocytes suggests its involvement in the pathogenesis of the disorder.
• The structural basis for DAF size variations and their link to PNH remains to be elucidated.